Rambus, a developer of chip interface products and memory, showcased functional XDR DRAM memory subsystems for the first time in history. While it is still remains to be seen whether the industry will try to taste Rambus again after RDRAM, the demonstration clearly indicates that Rsmbus' technologies are mature enough to be exposed and implemented into applications.

Rambus Touts XDR, DPP

XDR memory’s novel system topology allows point-to-point differential data interconnects to scale to multi-gigahertz speeds, while the bussed address and command signals allow a scalable range of memory system capacity supporting from 1 to 36 DRAM devices. XDR DRAMs will be available in multiple speed bins, device densities, and device widths. With densities ranging from 256Mb to 8Gb, and device widths ranging from x1 to x32, XDR DRAM satisfies the needs of both high-bandwidth and high-capacity systems, the company indicated.

Single-channel XDIMM memory system

“Once memory speeds surpass 1 gigahertz data rates, routing data busses to multiple upgradeable modules becomes a challenge,” said Rich Warmke, director of marketing for the Memory Interface Division at Rambus.

An indivisible part of XDR DRAM technology is Dynamic Point-to-Point (DPP) technology that allows memory systems to scale in terms of capacity without any potential affect of performance or need to reduce the clock of the memory sub-system.

Dual-channel XDIMM memory system

“To meet the future needs of the PC and home server memory markets, Rambus's DPP technology will be critical for OEMs who want to ship future high-performance memory-enabled PCs or home servers with a single module at full system bandwidth, with the option for a second module upgrade,” Mr. Warmke added.

XDIMM System Shown Off

A single XDR memory-enabled 32-bit XDIMM module provides 12.8GB/s working on 3.20GHz frequency. In dual-channel mode, a widely available way to plug-in memory modules today, such XDIMM system can provide twice bandwidth. In future a single 32-bit module has potential to provide 25.6GB/s when functioning at 6.40GHz.

XDIMM memory module

Toshiba has been sampling 512Mb XDR DRAM 3.20GHz devices since late 2003 and is on track to deliver the actual products in 2005 or 2006. Sony’s PlayStation 3 is expected to use XDR DRAM and is currently the most well-known XDR-based product.

Rambus GDDR3 memory system

XDIMM uses 6 or 8 layer PCBs, fits into typical DIMM’s, 5.25” x 1.375”, size envelope. XDIMM does not share RIMM infrastructure: even though it also uses 232-pin connector, the XDIMM modules locate key, a special slit that ensures correct memory installation, in a new place. Rambus said XDIMM interconnection topology requires 4 layer PCBs on mainboards.

RaSer Interface

In addition to dual-channel and single-channel XDIMM systems Rambus showcased its GDDR3 memory controller as well as RaSer PCI Express interconnection.